A T1 transmission line, also referred to as a DS1 line, is a dedicated telephone connection that may support data ranges of up to 1.544 Mbits per second (Mbps). A T1 line may have 24 individual channels, each of which support 64 Kbps. Each 64 Kbps channel may be configured to carry digital data that may represent voice or other types of analog data, or purely digital information.
E1 is the European format for digital transmission and is similar to the North American T1. E1 carries signals at 2.048 Mbps (32 channels at 64 Kbps). E1 and T1 lines may be interconnected for international use.
T1/E1 transceivers may receive and transmit digital signals over a telephone communication transmission line to a connecting communication system, for example, a business computer network. T1 (and E1) lines may be used as a leased line option for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone.
Data transmitted over a T1 line may be formatted in frames including a predetermined number of bits, e.g., 193 bits for a standard T1 frame 100, as shown in FIG. 1. The frame includes twenty-four 8-bit time slots 102, each corresponding to one of the twenty-four channels in the T1 line.
The information in the time slots may be switched by a cross connect over dedicated circuitry according to a switching table. Switching information over a cross connect may entail a certain switching delay. It may be desirable to connect two or more cross connects to switch signals between multiple transmission lines. However, connecting cross connects serially may increase the switching delay since the overall switching delay is cumulative, with each cross connect contributing. Also, each cross connect may be limited to a number of input ports. This may limit the cross connect""s access to information from transmission lines not directly input to that cross connect.